Question

what is the cause of the striated appearance of skeletal and cardiac muscle?

the arrangement of intercalated discs

the repeating arrangement of the contractile proteins, actin and myosin

the stacking of muscle cells

the nuclei of the muscle cells

the connections of neurons to muscle cells

Explanation:

1. Analyze each option:

• "the arrangement of intercalated discs": Intercalated discs are specific to cardiac muscle for cell - cell communication and do not cause striations.
• "the repeating arrangement of the contractile proteins, actin and myosin": In skeletal and cardiac muscle, actin (thin filaments) and myosin (thick filaments) are arranged in a repeating, highly organized pattern (sarcomeres). This regular arrangement gives the muscle its striated appearance when viewed under a microscope.
• "the stacking of muscle cells": Stacking of muscle cells does not lead to the striated look; it is about the internal protein arrangement.
• "the nuclei of the muscle cells": The nuclei (location or number) of muscle cells are not related to the striated appearance.
• "the connections of neurons to muscle cells": Neuromuscular junctions are for signal transmission, not for creating striations.

Answer:

the repeating arrangement of the contractile proteins, actin and myosin